linux-kernel - [for-next][PATCH 12/13] seq_buf: Add seq_buf

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Date:   Fri, 19 Mar 2021 14:34:38 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     linux-kernel@...r.kernel.org
Cc:     Ingo Molnar <mingo@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Yordan Karadzhov <y.karadz@...il.com>
Subject: [for-next][PATCH 12/13] seq_buf: Add seq_buf_terminate() API

From: "Steven Rostedt (VMware)" <rostedt@...dmis.org>

In the case that the seq_buf buffer needs to be printed directly, add a way
to make sure that the buffer is safe to read by forcing a nul terminating
character at the end of the string, or the last byte of the buffer if the
string has overflowed.

Signed-off-by: Steven Rostedt (VMware) <rostedt@...dmis.org>
---
 include/linux/seq_buf.h | 25 +++++++++++++++++++++++++
 1 file changed, 25 insertions(+)

diff --git a/include/linux/seq_buf.h b/include/linux/seq_buf.h
index 9d6c28cc4d8f..5b31c5147969 100644
--- a/include/linux/seq_buf.h
+++ b/include/linux/seq_buf.h
@@ -71,6 +71,31 @@ static inline unsigned int seq_buf_used(struct seq_buf *s)
 	return min(s->len, s->size);
 }
 
+/**
+ * seq_buf_terminate - Make sure buffer is nul terminated
+ * @s: the seq_buf descriptor to terminate.
+ *
+ * This makes sure that the buffer in @s is nul terminated and
+ * safe to read as a string.
+ *
+ * Note, if this is called when the buffer has overflowed, then
+ * the last byte of the buffer is zeroed, and the len will still
+ * point passed it.
+ *
+ * After this function is called, s->buffer is safe to use
+ * in string operations.
+ */
+static inline void seq_buf_terminate(struct seq_buf *s)
+{
+	if (WARN_ON(s->size == 0))
+		return;
+
+	if (seq_buf_buffer_left(s))
+		s->buffer[s->len] = 0;
+	else
+		s->buffer[s->size - 1] = 0;
+}
+
 /**
  * seq_buf_get_buf - get buffer to write arbitrary data to
  * @s: the seq_buf handle
-- 
2.30.1